Conservatives are facing a tough fight to limit the damage expected to be inflicted at next week's council polls, the Press Association's analysis of the contest shows.

The May 2 elections for 34 English top-tier counties and unitary authorities, plus the Isle of Anglesey in Wales, will be closely watched for early indications of the likely outcome of the next General Election in 2015. The voters eligible to take part make up nearly 40% of the UK total.

This year's battleground covers much of the Tory heartlands - 28 of the of the 35 authorities are currently theirs - but the party seems certain to lose many council seats in contests involving nearly 10,000 candidates.

Labour, with a double-digit lead in some opinion polls, is expected to make significant gains on a big swing back from its sweeping losses of 2009 when this year's defending councillors were last returned.

A PA calculation based on 13 comparable council by-election contests over April gave a projected 7% nationwide lead for the party over the Tories. It compares with a 15% Labour deficit in 2009.

Liberal Democrats have been making gains in council by-elections in recent months, mainly at the expense of the Tories. After victory against their coalition government partners at the Eastleigh parliamentary by-election, Lib Dem hopes of defending key council seats have risen - although they face losses overall.

Ukip has followed up its strong showing at Eastleigh, where it beat the Tories for second place, by fielding just 18 fewer candidates than the Lib Dems. Ukip has 1,745 against the Lib Dems' 1,763, while the Tories have 2,263 and Labour 2,168. Ukip has also had a run of recent council by-election gains.

There are mayoral elections at Doncaster, where former English Democrats Party member Peter Davies is standing again as an independent, and North Tyneside, where Tory incumbent Linda Arkley is seeking another term.

The South Shields by-election, prompted by Labour former Cabinet Minister David Miliband's resignation as MP to become head of the International Rescue Committee in New York, also takes place on May 2. South Shields is a safe Labour constituency, where Mr Miliband had a majority of 11,109 at the 2010 General Election.

A total of 2,449 seats are up for grabs in the council polls. There will also be by-elections for some councils not up for a main election this year.